Steve Jobs, the chief executive of Apple, is to take of leave of absence after disclosing that his health problems are "more complex than originally thought".

The 53-year-old, who survived a pancreatic scare five years ago, claimed earlier this month that his visible weight loss was due to a hormone imbalance that was relatively simple to treat.

But in a surprise announcement, the man whose vision and acumen made the iPod and iPhone must-have gadgets conceded that his condition was more serious, and said that he would step back from day-to-day role at the technology giant until the end of June.

Apple's chief operating officer Tim Cook will take over many of his responsibilities, but Mr Jobs will continue to be consulted on strategic decisions.

The statement from Mr Jobs, who has always been reluctant to publicly discuss his health, will revive speculation about how the firm he co-founded with Steve Wozniak in 1976 will fare without him, and the identities of his potential successors. He is seen as central to Apple's success, turning the loss-making company round after returning from a spell away in 1997.

Shares in Apple dipped by as much as 12 per cent in late trading in the US last night before recovering slightly, as the market digested the news.

In a message to staff, Mr Jobs wrote: "Unfortunately, the curiosity over my personal health continues to be a distraction not only for me and my family, but everyone else at Apple as well. In addition, during the past week I have learned that my health-related issues are more complex than I originally thought.

"In order to take myself out of the limelight and focus on my health, and to allow everyone at Apple to focus on delivering extraordinary products, I have decided to take a medical leave of absence until the end of June."

Speculation about Mr Jobs's health resurfaced in June 2008, when he appeared markedly thinner at an Apple event. He did not deliver his annual keynote address at the recent Macworld conference in San Francisco earlier this month, with his place being taken by executive Phil Schiller.